1. Field of the Invention
The present invention relates generally to the field of double walled storage tanks. More specifically, the present invention discloses an above-ground double walled storage tank having a spray apparatus fed by water circulated through the space between the inner and outer tanks for fire suppression.
2. Statement of the Problem
Double walled storage tanks are well known in the art for a wide variety of uses. In recent years, double walled tanks have increasingly been used for above ground storage of gasoline and other flammable liquids. This created a need for an effective means for fire suppression in such storage tanks. As will be discussed below, a number of prior art references teach that the temperature of the inner tank can be regulated by circulating a coolant, such as water, in the annular space between the tanks. However, none of these prior art references has apparently recognized that flooding the space between the tank with water can be entirely counterproductive if the inner tank has ruptured and is spilling gasoline or other flammable petroleum products into the space between the tanks. This situation merely tends to spread the blaze as the coolant is circulated out of the space.
A number of double walled storage tanks with temperature regulation systems or fire suppressions systems have been invented in the past, including the following:
______________________________________ Inventor U.S. Pat. No. Issue Date ______________________________________ Majors 4,993,497 Feb. 19, 1991 Gerhard 4,756,447 July 12, 1988 Simon 4,177,863 Dec. 11, 1979 DeBoer 3,896,881 July 29, 1975 Powell 3,019,843 Feb. 6, 1962 Bergstrom 2,687,618 Aug. 31, 1954 Clark 1,874,243 Aug. 30, 1932 Winkler U.K. Appln. Filed 6/15/78 2,000,022 ______________________________________
Majors discloses a deluge funnel tank jacket. A funnel shaped jacket is attached to a rib framing system that is strapped around the storage tank. In the event of fire, water is introduced at the top of the tank by the funnel and is then fed by gravity through the waterway formed between the funnel jacket and the tank shell.
Gerhard discloses a system using a fluid circulated in the jacket surrounding the inner tank to control temperature.
The Clark, Winkler, and Powell patents disclose double walled tanks that have an outer tank holding a fire suppressing liquid that is automatically released to control a fire in the inner storage tank.
Bergstrom discloses a storage system for liquefied hydrocarbons, such as propane or butane, in which a plurality of inner tanks are surrounded with water held in a single outer tank.
De Boer discloses an automatic fire extinguisher for a storage tank holding a flammable liquid. This system includes multiple reservoirs holding a fire extinguishing fluid that are activated at progressively higher temperatures to extend the time and quantity of fire extinguishing fluid available.
Simon discloses a safety liquid dispenser for holding a flammable liquid. A pressurized nonflammable gas, such as carbon dioxide, is held inside an intermediate container within the tank. The carbon dioxide can be selectively released into the tank to suppress any fire.
In addition to these prior art references, it should be noted that perhaps the most common method of fire fighting is to cool the exterior of the storage tank by spraying large quantities of water from a fire hose. However, the high pressure water hits the tank with such force that the water tends to immediately bounce back off the face of the tank. As a result, the water is in contact with the tank skin for only a short time and relatively inefficient in transferring heat because of this limited contact with the tank. Moreover, the fire fighter must position himself relatively closely to the tank and therefore exposes himself to increased peril.
3. Solution to the Problem
None of the prior art references uncovered in the search show a double walled storage tank having a spray apparatus fed by water circulated through the space between the inner and outer tanks. This circulation of water serves both to directly cool the inner tank by conductive heat transfer and to cool the entire assembly by the spray of water over the outer tank. In addition, the system includes a vapor sensor to detect leakage from the inner tank. In the event of leakage, the vapor sensor controls a valve in the outlet pipe that prevents flow to the spray apparatus, and instead directs the flow of coolant water and any entrained flammable liquid to a remote containment facility.